Industrial pulverizers of the roll-and-race type typically have grinding elements or roll wheels fixed in relation to the vertical axis of the pulverizer which bear upon a rotating track on a grinding table. The table is part of a yoke which is driven through a gear box by an electric motor. The area where the yoke penetrates the outer stationary case or housing of the pulverizer is sealed, often with an assembly comprising two seals, preferably labyrinth seals, and a compartment for sealing air. Sealing air, at a pressure higher than the internal pressure of the pulverizer, is introduced into the compartment and is allowed to exhaust at a controlled rate, both to the atmosphere and into the lower chamber of the pulverizer. Sealing air is supplied from the same source to the seals in the roll wheels. Sealing air serves two purposes: first, it prevents pulverized coal dust from entering the atmosphere through the yoke seal, and, secondly, it prevents coal dust from entering the bearings in the roll wheels which would cause premature failure of the bearings. Wear in the lower labyrinth seal around the yoke allows an increasing leakage to atmosphere which diminishes the sealing air available to the roll wheels. Increased leakage to atmosphere also causes increased operating temperatures in the vicinity of the gear box and motor and pollutes the atmosphere with coal dust.
At the present time, the only remedy for a failed labyrinth seal is to replace it. Replacement involves removal of the roll wheels, yoke and grinding table from the pulverizer, and removal of the gear box from under the pulverizer to allow sufficient clearance to remove the yoke seal assembly. Critical alignment parameters are disturbed in the process of disassembly and removal of components to gain access to the seal.